You can have calls go to a single extension for all inbound calls or to a ring group to ring a few phones. If still no answer you can do to another ext or ring group or to a Digital Receptionist to automate it. I do this in case the person can't pick up the phone in time it will still get answered.

On the subject of a human receptionist... all incoming calls made to our main office number are routed to the receptionist on extension 0. If she is busy however, calls are sent to a ring group so that any of our administrators can pick up the incoming call. In a case where the receptionist is busy and an administrator is to answer the phone, is there anyway of informing the administrator that the call they are about to answer is a call placed to the ring group and not just their personal extension?

This would be helpful so they can answer the phone "Hello... *business name*" instead of how they would answer a personal call that had arrived through their DDI.